Pretreatment of noncellulosic textiles



Patented July 1, 1947 John D. Pollard, Stamford, Conn.,.assignor toAmerican Cyanamid Company, New York, N. Y., a corporation of Maine NoDrawing. Application July 3, 1944,

Serial No. 543,427

Claims.

This invention relates to the bonding of textile filaments, fibers,threads, cords and fabrics composed of or containing non-cellulosicconstituents to coatings, and more particularly to the pretreatment ofsuch textiles to form an anchorage for coatings that may subsequently beapplied.

In my copending application, Serial No. 516,249, filed December 30,1943, I have shown that the bonding properties of cellulose andcellulosic textiles are improved by the application thereto of anacidified aqueous colloidal solution of partially polymerizedmelamine-formaldehyde resin. The present invention is the result of acontinuation of the investigation reported in that application, and isbased on my discovery that a simi- -lar improvement is obtained whennon-cellulosic textiles such as silk, nylon, wool, felted wool, caseinfibers and the like are pretreated with the same type of aqueous resinsolutions.

I have found that the bonding properties of non-cellulosic textiles inthe form of filaments, threads, fibers, fabrics and the like areimproved by the application thereto of an acidified aqueous colloidalsolution of partially polymerized melamine-formaldehyde resin. Althoughmy invention is not limited by any theory of operation, I believe thatthis remarkable improvement is due to a modification of the surfacecharacteristics of the textile fibers by the colloidalmelamineformaldehyde resin. This opinion is supported by the fact thateven minute quantities of colloidal, water-insoluble resin on the orderof 0.01% of the dry weight of the textiles will produce a great increasein bonding properties thereof, whereas a similar improvement is notobtained by impregnating the textiles with small or even moderatelylarge amounts of the same resin in an unpolymerized and water-solublecondition. My

invention in its broader aspects therefore comprises the step ofimpregnating non-cellulosic textiles of the type exemplified by wool,silk, and linear polymers such as nylon. casein and vinyon withacidified aqueous colloidal melamine-formaldehyde resin solutions underconditions such that the treated textile fibers contain small quantities on the order of Mil-2% of the resin in a wa- 'ter-insolublecondition; i. e., in such a form that the colloidal resin is not removedby washing the fibers with water immediately after impregnation. Theresin is then preferably cured on the textiles, as by heating, afterwhich they are in condition for coating by any known or approved coatingprocedure. Silk and nylon threads ing or impregnating materials haveheretofore been applied to threads, fibers, fabrics and the like. Thus,for example, a wide variety of waterproofing materials have been coatedupon silk,

nylon and similar fabrics in the production of raincoats, water-proofbags, light-weight tents,

gasproof clothing and the like. including such materials as natural orsynthetic rubber, cyclized rubber, chlorinated rubber, polyvinylbutyralcoatings including mixtures of polyvinyl butyral with alkydresins, aswell as synthetic resin compositions and the like. The presentinvention in its broader aspects is not limited to coated compositionscontaining any one or more coating materials, but is directed primarilyto a method ofpretreating the cellulosic material in such a manner as toimprove its bonding characteristics when coating materials are appliedthereto.

The aqueous colloidal solutions of partially polymerizedmelamine-formaldehyde resin which are used in practicing my inventionmay be prepared by any one of several different procedures. Amelamine-formaldehyde condensation product may-be dissolved in acidifiedwater which preferably contains sufiicient acid to produce a glasselectrode pH value within the range of about 0.5-4.0 when measured at12% resin solids content and the solution may then be aged at roomtemperature or at elevated temperatures until a hydrophilic colloid isformed. If desired, the aqueous solvent in which the resin is aged maycontain substantial quantities of a polyhydric alcohol such as glycerol,ethylene glycol and the like, but in this case it is not necessary touse such large quantities of acid and the desired hydrophilic colloidcan be obtained at pH values as high as 6.8, which means that thequantity of free acid in the solution is almost vanishingly small.However,-the resin solution must always contain some water (usually atleast 20% for best results) and it must always be acidified with atleast a minute quantity of acid, as otherwise the desired hydrophiliccolloid is not obtained.

Substantial quantities of acid are extremely undesirable in textiles. Itis therefore a very important advantage of my invention that thenecessary quantities of the colloidal melamine-form- 3 aldehyde resinare retained by the textile fibers in a waternsoluble condition, for thefibers can be washed ith water immediately after they have beenimpregnatedwith the resin. This washing step not only removes all theacid, but also removes water-soluble resin which would otherwise remainon the textiles and produce an undesiracid. and even such weak acidsneed beused in only very small quantities; The presence of weak acids inthe impregnated textiles in small quanties is not objectionable, andtherefore it is easy to deposit the requisite small quantities of thecolloidal resin on the textiles ina water-insoluble condition withoutdamaging the fibers.

It has'previously been proposed to apply melamine-formaldehyde resins totextile fabricsv in such quantities as to render them creaseproof or tofunction as adhesives for stiffening agents, filling agents, softeningagents, water-repellents and the like. In all such cases, however, themelamine resin has been employed as a physical bonding agent, andtherefore amounts on the order of have usually been impregnated into thefabrics.

-In such processes it is. of course. impossible to wash the fabricimmediately after the impregnation. as the adhesive qualities of theresin are developed only after it has been cured, and therefore the,acid employed as a solvent or curing agent is retained in the textiles.The present invention is based on the discovery that small quantitles ofcolloidal partially polymerized melamineformaldehyde resin on the orderof 0.01-2% of the weight of the non-cellulosic textiles will impartgreatly increased bonding properties to the fibers thereof and on thefurther important discovery that these quantities are retained by thefibers in a water-insoluble condition resistant to 'washing when thetextiles are impregnated with the acidified colloidal aqueous solutions.It is apparent. therefore, that the present invention accomplishesobjects which could not be attained by the processes of the prior artand is based on entirely different principles.

The presence of free acid in a textile material usually results in anundesirable degradation and loss in strength, and for this reason it is.very important to leave as little free acid as possible on the fibers.In practicing the present invention this may be done either bywashing'the textiles with water after the initial application of theresin solution. or by employing aqueous solutions containing-polyhydricalcohols such as glycerine,

ethylene glycol and the like containing very small quantities of acid.or both. In the lattercase the subsequent washing step is of course notprecluded, but the washing does not have to be as thorough as whenlarger quantities of acid are employed.

In view of the importance of avoiding the presence of substantialquantities of free acid on the textile fibers the resin retentionobtained with the colloidal, salt-sensitive melamine-formaldehyde resinsolutions is an extremely important feature of the invention. Nodimculty is encountered in obtaining retention of the extremely smallquantities of the colloidal resin on the order of 0.01-2% of the dryweight of the textiles that are sufilcient to produce a stronger bondwith coating materials, even after thorough washing with water. Largerquantities of applied resin are unnecessary and are usually undesirablesince they merely stiffen textiles without further improving theirbonding properties.

Ordinarily the aged colloidal melamine-formaldehyde resin solutions areapplied to the textiles at high dilutions on the order of 0.1-3%.although concentrations up to 6% and higher have been employed withsuccess. The more dilute solutions are usually preferred for severalreasons; first, because of greater economy in the use of resin,secondly. because less acid is taken up by the textiles from more dilutesolutions, and finally, because of the greater ease of washing theimpregnated textiles. The resin solution may also contain plasticizers,softeners, finishing agents or other compatible ingredients for thetextiles, such as polyvinyl alcohol, polyethylene oxide having amolecular weight of 1500-4000,

peratures as low as 70 F., although ordinarily higher temperatures up toabout 240 F. ar preferred because of the greater curing speed. It isevident, therefore, that no special curing equipment is necessary inpracticing the present invention; ordinary steam or hot air drires maybe employed and the curing of the resin may be accomplished at the sametemperatures and under the conditions that are usually employed to drythe textile fibers.

Some of the colloidal aqueous solutions of partially polymerizedmelamine-formaldehyde resin used in practicing the invention aredescribed in U. S. Patent No. 2,345,543, and may be prepared by any ofthe methods described in that patent. Another method of preparing thistype of resin consists in the formation of a hydrophobicmelamine-formaldehyde resin syrup, for example by reacting 115 pounds of37% aqueous fomalin with 59.5 pounds of melamine at a pH of 7.0 at IO-850., followed by spray-drying the product in a current of hot gases at420 F. Upon dissolving the spray dried product in water containing anequimolecular quantlty'of HCl to a solution containing 12% solids apartially polymerized resin solution is obtained without the necessityof extensive aging.

Numeroussolvents other than water may be used as dispersing agents formelamine-formaldehyde resins, and I have found that the resin can beconverted to the colloidal condition with the aid of much smallerquantities of aqueous acid when water-soluble dior polyhydric alcoholsor their ethers are present. Typical solvents of this class which may beused are ethylene glycol, glyceral, diglycerol, polyethylene glycols andtheir monoethers such as the monoethyl ether of ethylene glycol as wellas glucose and sucrose. Monohydric alcohols have been tested, but failto give satisfactory colloidal solutions .when reduced quantities ofaqueous acid are used.

several factors govern the optimum proportions to 3.5" by size, andbetween the two faces oi. oi polyhydric alcohols to be used. At a givenfabric is placed a 2" by 4" strip of uncured polyresin solid content,such as 12%, very concenvinyl butyral coating about .008"-thick. Athertrated aqueous solutions containing 80-95% of mosetting polyvinylbutyral coating composed of glycerol or ethylene glycol must be used todis- 5 vinyl butyral resin (6-'7% hydroxyl) plus curing solve the resinwhen no aqueous acid is present. resin, plasticized with triethyleneglycol octace- I1, however, an aqueous acid solution is used in tate andcastor oil was used in the tests described conjunction with thepolyhydricalcohol solvent below. The test piece is placed between twothe amount of alcohol can be reduced; thus with pieces of canton flanneland pressed for 30 sec- 0.1 mol of acetic acid per mol of resin only 60%1 onds at 60 C. and 190 pounds per square inch.

of the alcohol need be used. As the pH is re- The pressed piece is thencured for one hour duced the amount of alcohol necessary is also at 260F. without pressure.

reduced; for example, it 0.5 mol of acetic acid In testing'for drycoating adhesion, the test i used a 40% glycerine or ethylene glycolsolusamples are conditioned for 24 hours at 73 F., tion will serveasasolvent. 50% relative humidity and then pulled apart in The aging ofacidified solutions containing a aSchopper tensile testing machine.Similar tests high concentration of polyhydrlc alcohol is very for wetadhesion are conducted after soaking the low; in fact, the colloidalcondition isnot reached laminated pieces in water for 48 hours at roomin four months at room temperatures in a 12% temperature. Adhesionvalues are recorded as resin solution containing 95% glycerol, 1 mol theforce in po required to separate the two of HCl per mol of melamine and5% water. Howfabrics when pulled apart at a rate of 12" per ever, if thesolution is diluted to contain at minute.

least 20% of water the aging period is reduced 1 The results obtainedwith various pretreatto 24 hours or less at this high acidconcentraments of nylon cloth are given in the following tion, and thesame results are obtained with 5 table. The test pieces of cloth wereimmersed somewhat longer aging times when greatly rein the colloidalresin solution for ilve minutes, duced quantities of acid are used. Thisis shown squeezed out, and washed in running water for by the followingexperimental results, which were iive minutes. The pieces were thendried in obtained by aging 12% solutions of the partially tenteringframes for 10 minutes at 200 F. A polymerized, spray-dried resindescribed above control sample was immersed in plain water for at roomtemperature. the same length of time and dried along with Appearance oi1% dilutions Sam Mols'acid Solvent Used per mol pH resin nu Ida M 8-10 7days days Water 0.1 acetic... Notdispersible at 12%s0lids 00 aq.giycerolo 53 ppt--. col. col gel. 00 aq.glycol o 5.1 ppt.-. col.. col.. gel.00%aq.glycol 0.5acetic.. ,4.6 ppt--. 001.... 001.... gel. 607amgIyoei-oi. Noacid 7.2 ppt-.. ppt-.. ppt-.. ppt. 00 aq.glyceroi.0051101.... 5.5 ppt--. ppt col. col.

80%aq.glycerol .....do 54 ppt... 001.... 001.... clear.

The colloidal condition is reached in a considthe impregnated samples,and a second control erably shorter time when the above solutions aresample was laminated without washing. aged at -100 C., even when onlysmall quantitles of acid are used. Thus, for example, a 12% Per CentAdhesion,

lbs 2" resin solution in a solvent composed of Resin glycerol, 5% waterand 0.01 mol acetic acid per sogdghin wgm mol of melamine showedcolloidal properties upon .30 dilution with water to 1%, resin solidsafter only six hours aging at C. kg 3;: 3-3 The application of a largenumber of'aged 6.0 810 is melamine-formaldehyde resin solutions contain-3 g g if, ing aqueous glycol, glycerol and other water-solu- 1.0 10.03.0 ble polyhydroxy compounds to nylon fabrics has 3 Q2 shown thatsatisfactory retention is obtainable wi h y slightly polymeriz d r n butthat cfiifififfi 'sari:11111111111111:111111111111 i3? 3:3

in all cases at least a small amount of acid must h 1 r 60 be presentHowever t 889 so vents pe mit the A-l mol trimethylol melamine, 0.8 molHCl aged 4 hours at i2% reduction of th quantity f a id 0 th point resinsolids at room temperature, then diluted with water to theconcentrations used. where washing of the fabric is unnecessary A] 13-25grams trimethylol melamine, 23.6 grams ethylene 8150?], to or thoughthis is an advantage in the commercial 11.5 grams water and 2.4 gramsglacial acetic acid were hea 1.5 hours at 00 C. The solution was thendiluted with ethylene pretreatment of fabrics F must be emphasizedglycol to a total weight oi 200 grams, aged 4 hours, and diluted withthat the impregnating solution should not con- Water the 00110011080011usedtain more than a few percent of resin, on the What I claim order of0.56% or less as otherwise the fabric 1 l. A method of improving thebonding proper- Wm become stiffened when the resin 15 cm ties ofnon-cellulosic organic textiles which com- The mpmved adhesionobtainable by preheat 7 0 prises impregnating said textiles with anacidic Q mam of non'ceuuloslc textiles with partially aqueous colloidalsolution of melamine-formaldepolymenzed memmme'mrmamehyde resin hyderesin in a solvent comprising a water-soltions can readily bedemonstrated by the followm polyhydric alcohol and retaining o o me t tpr A mp of pretreated test of resin on the textiles in a water-insolubleconfabric, for example silk or nylon fabric, is folded 75 dition.

of 0.014% of the dry weight thereof.

3. A method of improving the bonding properties of non-cellulosicorganic textiles which comprises the steps oi impregnating said textilesin abath prepared by aging an aqueous solution tion.

' or a melamine-formaldehyde condensation product in a solventcomprising a polyhydric alcohol and suillcient acid to reduce the pH toabout 4.5- 6.8 until a colloidal melamine-formaldehyde resin solution isformed, whereby colloidal particles oi the 'resinare deposited on thetextiles in amounts 4. A method of improving the bonding proper. ties ofnylon textileswhich comprises impregnating them with an acidic aqueouscolloidal solution or melamine-iormaldehyde-resin in a solventcomprising a water-soluble polyhydric alcohol and. retaining 0.014% oi"resin on a waterpinsoluble condition.

5. A method oi improving the bonding properties oi non-cellulosicorganic textiles which The folio impregnating said textiles with anaqueous solution of colloidal melamine-formaldehyde resin in uble plyhydric alcohol and acid suiiicient to reduce rying the textiles and:resin on the fibers thereof.

a solvent comprising a water-sola small amount of the pH to 4.5-6.8 andcuring the water-insoluble J GEN D. POLLARD.

'naraaauoizs crran wing reierefices are of record in the iile of thispatent:

Number UNITED STATES PAW Name Date Widmer Feb. 20, 1940 Wolmsiedler Man28,' 1944 Widmer et al. May 80, 1944 Youna' Feb. 1, 1944 the nylon in

